Implantable stimulation devices are devices that generate and deliver electrical stimuli to body nerves and tissues for the therapy of various biological disorders, such as pacemakers to treat cardiac arrhythmia, defibrillators to treat cardiac fibrillation, cochlear stimulators to treat deafness, retinal stimulators to treat blindness, muscle stimulators to produce coordinated limb movement, spinal cord stimulators to treat chronic pain, cortical and deep brain stimulators to treat motor and psychological disorders, and other neural stimulators to treat urinary incontinence, sleep apnea, shoulder subluxation, etc. The description that follows will generally focus on the use of the invention within a Spinal Cord Stimulation (SCS) system, such as that disclosed in U.S. Pat. No. 6,516,227. However, the present invention may find applicability in any implantable medical device system.
As shown in FIGS. 1A and 1B, a SCS system typically includes an Implantable Pulse Generator (IPG) 100, which includes a biocompatible device case 30 formed of a conductive material such as titanium for example. The case 30 typically holds the circuitry and battery 26 necessary for the IPG to function, although IPGs can also be powered via external RF energy and without a battery. The IPG 100 is coupled to electrodes 106 via one or more electrode leads (two such leads 102 and 104 are shown), such that the electrodes 106 form an electrode array 110. The electrodes 106 are carried on a flexible body 108, which also houses the individual signal wires 112 and 114 coupled to each electrode. In the illustrated embodiment, there are eight electrodes on lead 102, labeled E1-E8, and eight electrodes on lead 104, labeled E9-E16, although the number of leads and electrodes is application specific and therefore can vary. The leads 102, 104 couple to the IPG 100 using lead connectors 38a and 38b, which are fixed in a non-conductive header material 36, which can comprise an epoxy for example.
As shown in FIG. 2, the IPG 100 typically includes an electronic substrate assembly 14 including a printed circuit board (PCB) 16, along with various electronic components 20, such as microprocessors, integrated circuits, and capacitors mounted to the PCB 16. Two coils (more generally, antennas) are generally present in the IPG 100: a telemetry coil 13 used to transmit/receive data to/from an external controller 12; and a charging coil 18 for charging or recharging the IPG's battery 26 using an external charger 50. The telemetry coil 13 is typically mounted within the header 36 of the IPG 100 as shown, and may be wrapped around a ferrite core 13′.
As just noted, an external controller 12, such as a hand-held programmer or a clinician's programmer, is used to wirelessly send data to and receive data from the IPG 100. For example, the external controller 12 can send programming data to the IPG 100 to dictate the therapy the IPG 100 will provide to the patient. Also, the external controller 12 can act as a receiver of data from the IPG 100, such as various data reporting on the IPG's status. The external controller 12, like the IPG 100, also contains a PCB 70 on which electronic components 72 are placed to control operation of the external controller 12. A user interface 74 similar to that used for a computer, cell phone, or other hand held electronic device, and including touchable buttons and a display for example, allows a patient or clinician to operate the external controller 12. The communication of data to and from the external controller 12 is enabled by a coil (antenna) 17.
The external charger 50, also typically a hand-held device, is used to wirelessly convey power to the IPG 100, which power can be used to recharge the IPG's battery 26. The transfer of power from the external charger 50 is enabled by a coil (antenna) 17′. For the purpose of the basic explanation here, the external charger 50 is depicted as having a similar construction to the external controller 12, but in reality they will differ in accordance with their functionalities as one skilled in the art will appreciate.
Wireless data telemetry and power transfer between the external devices 12 and 50 and the IPG 100 takes place via inductive coupling, and specifically magnetic inductive coupling. To implement such functionality, both the IPG 100 and the external devices 12 and 50 have coils which act together as a pair. In case of the external controller 12, the relevant pair of coils comprises coil 17 from the controller and coil 13 from the IPG 100. In case of the external charger 50, the relevant pair of coils comprises coil 17′ from the charger and coil 18 from the IPG 100.
When data is to be sent from the external controller 12 to the IPG 100 for example, coil 17 is energized with an alternating current (AC). Such energizing of the coil 17 to transfer data can occur using a Frequency Shift Keying (FSK) protocol for example, such as disclosed in U.S. Patent Publication 2009/0024179. Energizing the coil 17 produces a magnetic field, which in turn induces a voltage in the IPG's coil 13, which produces a corresponding current signal when provided a closed loop path. This voltage and/or current signal can then be demodulated to recover the original data. Transmitting data from the IPG 100 to the external controller 12 occurs in essentially the same manner.
When power is to be transmitted from the external charger 50 to the IPG 100, coil 17′ is again energized with an alternating current. Such energizing is generally of a constant frequency, and may be of a larger magnitude than that used during the transfer of data, but otherwise the basic physics involved are similar.
The IPG 100 can also communicate data back to the external charger 50 by modulating the impedance of the charging coil 18. This change in impedance is reflected back to coil 17′ in the external charger 50, which demodulates the reflection to recover the transmitted data. This means of transmitting data from the IPG 100 to the external charger 50 is known as Load Shift Keying (LSK), and is useful to communicate data relevant during charging of the battery 26 in the IPG 100, such as the capacity of the battery, whether charging is complete and the external charger can cease, and other pertinent charging variables. LSK communication from an IPG 100 to an external charger is discussed further in U.S. Patent Publication 2010/0179618.
As is well known, inductive transmission of data or power can occur transcutaneously, i.e., through the patient's tissue 25, making it particularly useful in a medical implantable device system. During the transmission of data or power, the coils 17 and 13, or 17′ and 18, preferably lie in planes that are parallel, along collinear axes, and with the coils as close as possible to each other. Such an orientation between the coils 17 and 13 will generally improve the coupling between them, but deviation from ideal orientations can still result in suitably reliable data or power transfer.
IPG 100 can comprise circuitry that enables a user or a clinician to shutdown the IPG 100 in case of emergencies. Such emergencies can arise when the IPG 100 malfunctions, undesirably over-stimulates the patient, does not provide stimulation at all, etc. FIG. 3 shows circuitry 302 that is traditionally used in the IPG 100 for emergency shutdown. A user or clinician brings a magnet 300 near the location on the patient's body where the IPG 100 is situated. A magnet sensor 306, such as a reed switch, detects the presence of magnet 300 by way of sensing its magnetic field, and sends an electrical signal (voltage or current) to a signal conditioning circuit 308. The signal conditioning circuit 308 suppresses any stray and transient signals (e.g., reed bounce) received from the magnet sensor 306. Once a sufficient signal indicating presence of magnet 300 is detected, the signal conditioning circuit 308 outputs a signal that opens switch 310. Once switch 310 is open, Rest of the Device (ROD) 312 will be disconnected from battery 26. ROD 312 will typically include all the circuitry responsible for the functioning of the IPG 100. For example, ROD 312 can include the microprocessor, charging circuits, telemetry circuits, stimulation circuits, volatile and non-volatile memory, etc. Upon being disconnected from the battery, these circuits will cease to function.
Although the aim of an emergency stop may be to immediately halt any stimulation being received by the IPG 100, an abrupt shut down like the one depicted in FIG. 3, can have certain disadvantages. For example, any data stored in volatile memory (e.g., RAM) will be lost, which data may include current stimulation program parameters. If the current stimulation parameters were intended to be stored/saved in non-volatile memory (into a stimulation parameter file, for example), an abrupt power loss may prevent the microprocessor from completing the save operation. In other instances it is also possible that the microprocessor is in the process of moving data from volatile memory to non-volatile memory when power loss occurs. This may result in only a partial data store—possibly corrupting the data stored in non-volatile memory.
In other instances it may be beneficial, from an analysis point of view, to record data relevant to the emergency shutdown itself. However, an abrupt shutdown may not allow the microprocessor to log this information into non-volatile memory.
A solution to this problem is provided in this disclosure in the form of an improved emergency shutdown circuit for an IPG 100 or other implantable medical device.